Pulling over to watch the rain and a motor biker colliding with the car and dying four hours later
If the reality is as you mentioned, you must make
kaffarah. It is to emancipate a believing slave, and if you are unable, you have to fast for two consecutive months, for Allah (Exalted be He) says:
...and whosoever kills a believer by mistake, (it is ordained that) he must set free a believing slave
And whoso finds this (the penance of freeing a slave) beyond his means, he must fast for two consecutive months
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.